Electronic component placement machines, sometimes called pick-and-place machines, are known. They are typically used to load chip components onto a printed circuit board (PCB) for subsequent processing, such as by soldering the components to the PCB traces.
The typical machine comprises a platform for supporting the PCB--usually supplied on a conveyor--adjacent to which are provided a plurality of component parts feeders. The components typically are provided on reels of tape supplied to the feeders or as stick or bulk feeders. A head movable in the X-Y plane, parallel to the PCB, and along the Z-axis, up and down with respect to the PCB, has at its bottom one or more parts holders which include pipettes, because the holding power is provided by computer-controlled suction. Attached to an active pipette is a gripper. Grippers are typically selective, only able to pick up certain sized parts.
To improve production throughput, it is desirable to reduce the time to load or populate the PCB. When the machine uses a single head with a single pipette, the problem reduces to locating the parts around the platform to minimize the distance the head has to move to pick up a part from a feeder and place it on its correct site on the PCB under computer control. Even though only one part at a time is picked and placed, providing an optimal or near-optimal parts layout-- known as configuring the machine--can be difficult, but is usually done by hand or by relatively simple conventional programs.
However, newer machines available on the market use multiple pipettes so that plural parts can be picked and place during each head movement. The problem then becomes assigning parts to the appropriate feeders, and grippers to pipettes, and one or more head-routing problems such as to minimize the time needed to populate the PCB. We refer to the assignment of parts to feeders and grippers to pipettes as a "layout" and the "charge map" as the specification of a control program for the machine. The combinatorial difficulties of this problem will be evident especially considering that a modern machine may have 28 pipettes, 112 bins or parts feeders, and a plurality of grippers capable of handling parts varying in size from 8-44 mm. In addition, other constraints on the machine configuration have to be taken into account, such as larger parts may require an additional alignment step, large parts in one bin feeder may shadow adjacent bin feeders which thus cannot be used, etc.
Manual solutions, on a trial and error basis, normally are used to establish a machine configuration for each new PCB layout. This is time consuming, and it is difficult to judge whether the configuration chosen is optimal. Some limited computer assistance is available for some machines. To our knowledge, no one has been able to develop a good computer-controlled algorithm capable of providing a near-optimal configuration for such a kind of placement machine employing multiple pipettes.